A composite material composed of a carbon fiber and a resin has a lightweight, a high strength, a high elastic modulus, etc. and, for these reasons, is in wide use in aeroplane, sports, leisure, and general industry. The composite material is manufactured, in many cases, via a prepreg in which a carbon fiber and a resin are integrated.
A thermosetting resin or a thermoplastic resin is used as the resin which constitutes the prepreg. There is widely used a prepreg which uses, in particular, a thermosetting resin because it can give a prepreg of high in tackiness, draping property and moldability. However, since a thermosetting resin has low toughness generally, a composite material manufactured using a prepreg composed of such a thermosetting resin has low impact resistance generally.
The methods described in Patent Literatures 1 to 5 are known for improvement of the impact resistance of such a composite material.
The Patent Literature 1 discloses a resin composition improved in toughness by dissolution of a thermoplastic resin in a thermosetting resin. In this resin composition, the toughness is improved correspondingly with the amount of the thermoplastic resin dissolved. Accordingly, a large amount of a thermoplastic resin need be dissolved in a thermosetting resin in order to obtain a resin composition of sufficiently high toughness. However, a thermosetting resin having a large amount of a thermoplastic resin dissolved therein has a very high viscosity, making it difficult, in the manufacturing of a prepreg, to impregnate a sufficient amount of a resin into a reinforcing fiber substrate. A composite material manufactured using a prepreg in which a sufficient amount of a resin is not impregnated into a reinforcing fiber substrate, has many defects such as void and the like. Consequently, such a composite material has problems in compressibility, damage allowance, etc.
The Patent Literatures 2 to 4 disclose prepregs obtained by localizing fine particles of a thermoplastic resin on the surface of a prepreg composed of a reinforcing fiber and a thermosetting resin composition. These prepregs have a particulate thermoplastic resin on the surfaces and accordingly are low in initial tackiness. Further, in these prepregs, since the curing reaction of thermosetting resin composition proceeds with time, the tackiness and draping property decrease with time. A composite material manufactured using a prepreg in which a curing reaction has proceeded, has many defects such as void and the like. Consequently, a composite material manufactured using a prepreg in which a curing reaction has proceeded, is significantly low in mechanical properties.
The Patent Literature 5 discloses a prepreg in which a thermoplastic resin having a particulate, fibrous or filmy shape is present in the vicinity of one or both surfaces of a prepreg. When a thermoplastic resin having a particulate or fibrous shape is used, the prepreg obtained has low tackiness and the composite material obtained has low mechanical properties, due to the same reasons as mentioned with respect to the Patent Literatures 2 to 4. When a thermoplastic resin having a filmy shape is used, the tackiness and draping property which are merits of thermosetting resin, are lost. Further, the defects such as low solvent resistance and the like, derived from the thermoplastic resin are strikingly reflected in the composite material obtained.